Tracy, what I think is going on with your well pump
is it is driven by a "universal AC motor". It has been years
since I studied these things so I am not sure about all this.

As I recall a universal AC motor, unlike a synchronous AC motor,
will speed up with no torque load. If the pump supply is
restricted the motor speeds up and the pump cavitates. 
You must prime the pump again by restricting output until
the motor loads up and slows down to below cavitation speed
and the pump then starts pumping again.

An engine water pump on the other hand runs at a fixed speed
relative to the e-shaft RPM depending on the pulley ratio.

Universal AC motors are a lot like DC motors in this regard
and they are widely used in hand tools. You will notice your 
hand drill slow down when encountering resistance. Synchronous 
motors on the other hand run at a fixed RPM depending on the line 
frequency and are found in lathes, drill presses, dryers and 
washing machines.

I could be way wrong.

Paul Lamar
 
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